The present invention relates to an internal combustion engine and an EGR heat exchanger for it.
There exist internal combustion engines comprising:                an intake manifold to receive and collect gas to be burnt in an engine cylinder and an exhaust manifold to collect and output exhaust gas from the engine cylinder,        a first turbocharger to compress air to allow more air to fill the engine cylinder, the turbocharger including a first turbine that transforms the exhaust gas flow into mechanical energy to actuate an air-compressor, the turbine having a turbine inlet fluidly connected to the exhaust manifold to receive exhaust gas that operates the turbine and a turbine outlet to output the exhaust gas used to operate the first turbine, and        an EGR (Exhaust Gas Recirculation) device to recirculate exhaust gas, the EGR device comprising an EGR heat exchanger having:        an exchanger inlet fluidly connected to the exhaust manifold through an EGR valve to receive warm EGR gas,        an exchanger outlet fluidly connected to the intake manifold to output cooled EGR gas,        a cooling medium inlet to receive a coolant, and        a cooling medium outlet to output the coolant once it has been used to cool the EGR gas.        
The existing internal combustion engines may also have a second turbocharger fluidly connected with the first turbocharger to further compress air. Turbochargers are pressure charging devices that further improves engine efficiency by using energy in an exhaust gas to provide pressure charging. Pressure charging an internal combustion engine both increases power and increases efficiency. Pressure charging is a process in which ambient air is compressed to allow more air to fill an engine cylinder. High pressure, high temperature exhaust gas enter a turbine connected to a compressor. As the high pressure, high temperature exhaust gas expands through the turbine, the turbine operates the compressor. As shown in U.S. Pat. No. 3,250,068 issued to Vulliamy on May 10, 1966 shows using turbochargers arranged in a serial fashion. This arrangement allows the turbochargers to be more responsive over a larger operative range and to further increase air pressure in the inlet manifold.
To reduce emissions, the exhaust gas recirculation (EGR) device is used for controlling the generation of undesirable pollutant gases in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines. EGR systems primarily recirculate exhaust gas from combustion into the intake air supply of the internal combustion engine. Exhaust gas introduced to the engine cylinder displaces a volume available for fresh air. Reduced oxygen concentrations lower maximum combustion temperatures within the cylinder and slow chemical reactions of the combustion process, decreasing the formation of nitrogen oxides (NOx), for example. Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder. Burning the unburned hydrocarbons further reduces the emission of undesirable pollutants from the internal combustion engine.
Cooling recirculated exhaust gas further enhances emissions reductions available through recirculating exhaust gas. Cooling the exhaust gas prior to introduction into the engine cylinder further reduces the combustion temperatures in the engine cylinder. As with lower oxygen concentrations, the reduced temperature of recirculated exhaust gas ultimately lowers production of NOx in the engine cylinder, for example.
For instance, such an engine is known from U.S. Pat. No. 6,360,732 in the name of Bailey et al.
Many of the internal combustion engine vehicles have also exhaust gas after-treatment device to clean exhaust gas before releasing it into the atmosphere. Well-known after-treatment devices are continuously re-generated diesel particulate filter or SCR (Selective Catalyse Reduction) mufflers. These after-treatment devices work correctly if the temperature of the exhaust gas to be treated is above a given threshold (300° C. for instance). For example, after starting the engine or when the vehicle speed is very low, the temperature of the exhaust gas that flows through the after-treatment device is much lower than 300° C. In those conditions, the exhaust gas cleaning is not as good as when the exhaust gas temperature is above 300° C.
It is desirable to provide an internal combustion engine that releases exhaust gas with a higher temperature than usual to improve exhaust gas cleaning, for example.
The invention provides, according to an aspect thereof, an internal combustion engine wherein the cooling medium inlet is fluidly connected to the turbine outlet so as to use the exhaust gas outputted by the turbine as the coolant.
In the above engine, the exhaust gas that flows to the after-treatment device is warmer than if exhaust gas was not used as a coolant in the heat exchanger.
Therefore, this helps the exhaust gas after treatment device to work by increasing the exhaust gas temperature. This also decreases the temperature of EGR gas so that the performance of the engine is increased.
The embodiments of the above engine may comprise one or several of the following features:                the EGR device comprises an EGR cooler which is fluidly connected to the exchanger outlet to cool the EGR gas outputted from the exchanger outlet before readmitting it into the intake manifold, the EGR cooler using a coolant which is different from exhaust gas;        the EGR cooler is also fluidly connected to an outlet of the first turbocharger to receive compressed fresh air and wherein the EGR cooler has a common internal chamber to mix together EGR gas and compressed fresh air as well as to cool EGR gas and compressed fresh air;        the engine comprises a second turbocharger to compress the air that is to be further compressed by the first turbocharger, the second turbocharger including a second turbine that transforms the exhaust gas flow into mechanical energy to actuate a second air-compressor, this second turbine having a turbine inlet to receive exhaust gas that operates the turbine and a turbine outlet to output the exhaust gas used to operate the second turbine, wherein the cooling medium outlet of the EGR heat exchanger is fluidly connected to the turbine inlet of the second turbine or wherein the cooling medium inlet of the EGR heat exchanger is fluidly connected to the turbine outlet of the second turbine to receive the exhaust gas successively expanded by the first and second turbine. The above embodiments of the engine present the following advantages:        using an EGR cooler further decreases the EGR gas temperature so that the engine performance increases and the EGR heat exchanger acts as a pre-cooler and relieves the technical constraints that are used to dimension and build the EGR cooler;        using the EGR heat exchanger to heat the exhaust gas that operates the second turbine of the second turbocharger increases the quantity of mechanical energy that the second turbine retrieves from the exhaust gas flow;        using the exhaust gas released at the outlet of the second turbine improves the efficiency of the EGR heat exchanger because exhaust gas at this outlet is colder than at the outlet of the first turbine. The invention also relates to an EGR heat exchanger suitable to be used in the above internal combustion engine.        
The invention also relates to a method to operate the above internal combustion engine wherein it comprises the step of admitting exhaust gas outputted by the turbine outlet of the first turbine through the cooling medium inlet so as to use the exhaust gas outputted by the first turbine as a coolant.
These and other aspects of the invention will be apparent from the following description, and drawings.